1. Field of the Invention
This invention relates to methods and apparatus for the photothermal treatment of tissue and, more particularly, to methods and apparatus for photothermal treatment of at least a selected region of tissue located starting at a depth at about the boundary zone of dermal and subdermal tissue and extending therebelow.
2. Description of the Related Art
The benefits of being able to raise and/or lower the temperature in a selected region of tissue for various therapeutic and cosmetic purposes has been known for some time. For instance, heated pads or plates or various forms of electromagnetic radiation, including microwave radiation, electricity, infrared radiation and ultrasound have previously been used for heating subdermal muscles, ligaments, bones and the like to, for example, increase blood flow, to otherwise promote the healing of various injuries and other damage, and for various therapeutic purposes, such as frostbite or hyperthermia treatment, treatment of poor blood circulation, physical therapy, stimulation of collagen, cellulite treatment, adrenergic stimulation, wound healing, psoriasis treatment, body reshaping, non-invasive wrinkle removal, etc. The heating of tissues has also been utilized as a potential treatment for removing cancers or other undesired growths, infections and the like. Heating may be applied over a small localized area, over a larger area, for example to the hands or feet, or over larger regions of tissue, including the entire body.
Since most of the techniques described above involve applying energy to tissue at depth through the patient's skin surface, peak temperature generally occurs at or near the patient's skin surface and decrease, sometimes significantly, with depth. Further, while microwaves or ultrasonic and other acoustic radiation have been used in the past for certain heating treatments at depth, as disclosed in, for example, U.S. Pat. No. 5,871,524 to Knowlton, U.S. Pat. No. 5,769,879 to Richards, et al., U.S. Pat. No. 5,507,790 to Weiss, or U.S. Pat. No. 5,143,063 to Fellner, since such radiation, particularly microwaves, are potentially mutagenic and can otherwise result in cell or systemic damage and, particularly for acoustic sources, are relatively expensive, and may not be practical for large-area treatment, these techniques have had limited use for the heating of tissues.
While optical and near infrared (NIR) radiation (collectively referred to hereinafter as “optical radiation” is generally both less expensive and, being non-mutagenic, safer than microwaves radiation, the use of optical radiation has heretofore not been considered suitable for most applications involving heating of tissue at depth, the term “tissue at depth” as used herein meaning tissue at the border zone of the dermis and hypodermis, some of which tissue may be in the lower dermis, mostly at a depth deeper than 1 mm, and tissue below this border zone to a depth of up to about 50 mm The reason why this radiation has not been considered suitable is because such radiation is both highly scattered and highly absorbed in surface layers of tissue, precluding significant portions of such radiation from reaching the tissue regions at depth to cause heating thereof. In view of the energy losses due to scattering and absorption, substantial optical (including NIR) energy must be applied in order for enough such energy to reach a region of tissues at depth to have a desired effect. However, such high energy can cause damage to the surface layers of tissue, making it difficult to achieve desired photothermal treatments in tissue regions at depth. For these reasons, optical radiation has heretofore had at most limited value for therapeutic and cosmetic treatments on tissue at depth.
Further, while heating of tissue at depth alone is useful for many treatments, there are treatments, for example to relieve pain and stiffness in muscles or joints, where heating in conjunction with massage or other mechanical stimulation, ultrasound or other acoustic stimulation or electrical stimulation of the tissue may also be useful.
Thus, a need exists for improved method and apparatus for photothermal treatment of tissue regions at depth, and in particular for treatment of subdermal regions of tissue, and for method and apparatus for combining heating with stimulation in such regions for various treatments.